Skip to content

L
linux
Switch branch/tag
  1. 08 Jun, 2022 3 commits
    • Jason Ekstrand's avatar
      dma-buf: Add an API for importing sync files (v10) · 59474049
      Jason Ekstrand authored 
      This patch is analogous to the previous sync file export patch in that
it allows you to import a sync_file into a dma-buf.  Unlike the previous
patch, however, this does add genuinely new functionality to dma-buf.
Without this, the only way to attach a sync_file to a dma-buf is to
submit a batch to your driver of choice which waits on the sync_file and
claims to write to the dma-buf.  Even if said batch is a no-op, a submit
is typically way more overhead than just attaching a fence.  A submit
may also imply extra synchronization with other work because it happens
on a hardware queue.

In the Vulkan world, this is useful for dealing with the out-fence from
vkQueuePresent.  Current Linux window-systems (X11, Wayland, etc.) all
rely on dma-buf implicit sync.  Since Vulkan is an explicit sync API, we
get a set of fences (VkSemaphores) in vkQueuePresent and have to stash
those as an exclusive (write) fence on the dma-buf.  We handle it in
Mesa today with the above mentioned dummy submit trick.  This ioctl
would allow us to set it directly without the dummy submit.

This may also open up possibilities for GPU drivers to move away from
implicit sync for their kernel driver uAPI and instead provide sync
files and rely on dma-buf import/export for communicating with other
implicit sync clients.

We make the explicit choice here to only allow setting RW fences which
translates to an exclusive fence on the dma_resv.  There's no use for
read-only fences for communicating with other implicit sync userspace
and any such attempts are likely to be racy at best.  When we got to
insert the RW fence, the actual fence we set as the new exclusive fence
is a combination of the sync_file provided by the user and all the other
fences on the dma_resv.  This ensures that the newly added exclusive
fence will never signal before the old one would have and ensures that
we don't break any dma_resv contracts.  We require userspace to specify
RW in the flags for symmetry with the export ioctl and in case we ever
want to support read fences in the future.

There is one downside here that's worth documenting:  If two clients
writing to the same dma-buf using this API race with each other, their
actions on the dma-buf may happen in parallel or in an undefined order.
Both with and without this API, the pattern is the same:  Collect all
the fences on dma-buf, submit work which depends on said fences, and
then set a new exclusive (write) fence on the dma-buf which depends on
said work.  The difference is that, when it's all handled by the GPU
driver's submit ioctl, the three operations happen atomically under the
dma_resv lock.  If two userspace submits race, one will happen before
the other.  You aren't guaranteed which but you are guaranteed that
they're strictly ordered.  If userspace manages the fences itself, then
these three operations happen separately and the two render operations
may happen genuinely in parallel or get interleaved.  However, this is a
case of userspace racing with itself.  As long as we ensure userspace
can't back the kernel into a corner, it should be fine.

v2 (Jason Ekstrand):
 - Use a wrapper dma_fence_array of all fences including the new one
   when importing an exclusive fence.

v3 (Jason Ekstrand):
 - Lock around setting shared fences as well as exclusive
 - Mark SIGNAL_SYNC_FILE as a read-write ioctl.
 - Initialize ret to 0 in dma_buf_wait_sync_file

v4 (Jason Ekstrand):
 - Use the new dma_resv_get_singleton helper

v5 (Jason Ekstrand):
 - Rename the IOCTLs to import/export rather than wait/signal
 - Drop the WRITE flag and always get/set the exclusive fence

v6 (Jason Ekstrand):
 - Split import and export into separate patches
 - New commit message

v7 (Daniel Vetter):
 - Fix the uapi header to use the right struct in the ioctl
 - Use a separate dma_buf_import_sync_file struct
 - Add kerneldoc for dma_buf_import_sync_file

v8 (Jason Ekstrand):
 - Rebase on Christian König's fence rework

v9 (Daniel Vetter):
 - Fix -EINVAL checks for the flags parameter
 - Add documentation about read/write fences
 - Add documentation about the expected usage of import/export and
   specifically call out the possible userspace race.

v10 (Simon Ser):
 - Fix a typo in the docs
Signed-off-by: default avatarJason Ekstrand <jason@jlekstrand.net>
Signed-off-by: default avatarJason Ekstrand <jason.ekstrand@intel.com>
Signed-off-by: default avatarJason Ekstrand <jason.ekstrand@collabora.com>
Reviewed-by: default avatarChristian König <christian.koenig@amd.com>
Reviewed-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: default avatarSimon Ser <contact@emersion.fr>
Link: https://patchwork.freedesktop.org/patch/msgid/20220608152142.14495-3-jason@jlekstrand.net
      59474049
    • Jason Ekstrand's avatar
      dma-buf: Add an API for exporting sync files (v14) · 20e10881
      Jason Ekstrand authored 
      Modern userspace APIs like Vulkan are built on an explicit
synchronization model.  This doesn't always play nicely with the
implicit synchronization used in the kernel and assumed by X11 and
Wayland.  The client -> compositor half of the synchronization isn't too
bad, at least on intel, because we can control whether or not i915
synchronizes on the buffer and whether or not it's considered written.

The harder part is the compositor -> client synchronization when we get
the buffer back from the compositor.  We're required to be able to
provide the client with a VkSemaphore and VkFence representing the point
in time where the window system (compositor and/or display) finished
using the buffer.  With current APIs, it's very hard to do this in such
a way that we don't get confused by the Vulkan driver's access of the
buffer.  In particular, once we tell the kernel that we're rendering to
the buffer again, any CPU waits on the buffer or GPU dependencies will
wait on some of the client rendering and not just the compositor.

This new IOCTL solves this problem by allowing us to get a snapshot of
the implicit synchronization state of a given dma-buf in the form of a
sync file.  It's effectively the same as a poll() or I915_GEM_WAIT only,
instead of CPU waiting directly, it encapsulates the wait operation, at
the current moment in time, in a sync_file so we can check/wait on it
later.  As long as the Vulkan driver does the sync_file export from the
dma-buf before we re-introduce it for rendering, it will only contain
fences from the compositor or display.  This allows to accurately turn
it into a VkFence or VkSemaphore without any over-synchronization.

By making this an ioctl on the dma-buf itself, it allows this new
functionality to be used in an entirely driver-agnostic way without
having access to a DRM fd. This makes it ideal for use in driver-generic
code in Mesa or in a client such as a compositor where the DRM fd may be
hard to reach.

v2 (Jason Ekstrand):
 - Use a wrapper dma_fence_array of all fences including the new one
   when importing an exclusive fence.

v3 (Jason Ekstrand):
 - Lock around setting shared fences as well as exclusive
 - Mark SIGNAL_SYNC_FILE as a read-write ioctl.
 - Initialize ret to 0 in dma_buf_wait_sync_file

v4 (Jason Ekstrand):
 - Use the new dma_resv_get_singleton helper

v5 (Jason Ekstrand):
 - Rename the IOCTLs to import/export rather than wait/signal
 - Drop the WRITE flag and always get/set the exclusive fence

v6 (Jason Ekstrand):
 - Drop the sync_file import as it was all-around sketchy and not nearly
   as useful as import.
 - Re-introduce READ/WRITE flag support for export
 - Rework the commit message

v7 (Jason Ekstrand):
 - Require at least one sync flag
 - Fix a refcounting bug: dma_resv_get_excl() doesn't take a reference
 - Use _rcu helpers since we're accessing the dma_resv read-only

v8 (Jason Ekstrand):
 - Return -ENOMEM if the sync_file_create fails
 - Predicate support on IS_ENABLED(CONFIG_SYNC_FILE)

v9 (Jason Ekstrand):
 - Add documentation for the new ioctl

v10 (Jason Ekstrand):
 - Go back to dma_buf_sync_file as the ioctl struct name

v11 (Daniel Vetter):
 - Go back to dma_buf_export_sync_file as the ioctl struct name
 - Better kerneldoc describing what the read/write flags do

v12 (Christian König):
 - Document why we chose to make it an ioctl on dma-buf

v13 (Jason Ekstrand):
 - Rebase on Christian König's fence rework

v14 (Daniel Vetter & Christian König):
 - Use dma_rev_usage_rw to get the properly inverted usage to pass to
   dma_resv_get_singleton()
 - Clean up the sync_file and fd if copy_to_user() fails
Signed-off-by: default avatarJason Ekstrand <jason@jlekstrand.net>
Signed-off-by: default avatarJason Ekstrand <jason.ekstrand@intel.com>
Signed-off-by: default avatarJason Ekstrand <jason.ekstrand@collabora.com>
Acked-by: default avatarSimon Ser <contact@emersion.fr>
Reviewed-by: default avatarChristian König <christian.koenig@amd.com>
Reviewed-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: default avatarSimon Ser <contact@emersion.fr>
Link: https://patchwork.freedesktop.org/patch/msgid/20220608152142.14495-2-jason@jlekstrand.net
      20e10881
    • Thomas Zimmermann's avatar
      drm/ast: Support multiple outputs · 7f35680a
      Thomas Zimmermann authored 
      Systems with AST graphics can have multiple output; typically VGA
plus some other port. Record detected output chips in a bitmask and
initialize each output on its own.

Assume a VGA output by default and use SIL164 and DP501 if available.
For ASTDP assume that it can run in parallel with VGA.

Tested on AST2100.

v3:
	* define a macro for each BIT(ast_tx_chip) (Patrik)
v2:
	* make VGA/SIL164/DP501 mutually exclusive
Signed-off-by: default avatarThomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: default avatarPatrik Jakobsson <patrik.r.jakobsson@gmail.com>
Fixes: a59b0264 ("drm/ast: Initialize encoder and connector for VGA in helper function")
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Javier Martinez Canillas <javierm@redhat.com>
Cc: Dave Airlie <airlied@redhat.com>
Cc: dri-devel@lists.freedesktop.org
Link: https://patchwork.freedesktop.org/patch/msgid/20220607092008.22123-2-tzimmermann@suse.de
      7f35680a
  3. 07 Jun, 2022 13 commits
  5. 06 Jun, 2022 1 commit
  7. 03 Jun, 2022 2 commits
  9. 02 Jun, 2022 12 commits
  11. 01 Jun, 2022 1 commit
  13. 31 May, 2022 1 commit
  15. 30 May, 2022 7 commits
GitLab Nexedi Edition | About GitLab | About Nexedi | 沪ICP备2021021310号-2 | 沪ICP备2021021310号-7